| | Williamstown, MI | South Lyon, MI | United States |
| Population | 5,282 | 11,786 | 329,725,481 |
| Female Population | 50.8% | 53.4% | 50.5% |
| Male Population | 49.2% | 46.6% | 49.5% |
| Median Age | 48.9 | 43.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 4,975 | 11,327 | 309,327,143 |
| Population - 2000 | 4,834 | 10,036 | 285,036,114 |
| Population - 1990 | 4,285 | 5,857 | 251,960,433 |
| Pop. 2000 to Now | 6.7% | 18.0% | 15.6% |
| Pop. 1990 to Now | 20.4% | 102.3% | 30.8% |
| space4 | | | |
| Population Density | 181.6 | 3,150.5 | 93.4 |
| Land Area | 29.1 | 3.7 | 3,531,905.4 |
| Water Area | 0.2 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Williamstown, MI | South Lyon, MI | United States |
| Age 0 to 4 | 4.8% | 4.5% | 5.9% |
| Age 5 to 9 | 6.1% | 6.4% | 6.1% |
| Age 10 to 14 | 4.8% | 6.3% | 6.6% |
| Age 15 to 17 | 6.0% | 3.3% | 3.9% |
| Age 18 to 20 | 2.6% | 4.0% | 4.0% |
| Age 21 to 24 | 3.4% | 6.2% | 5.2% |
| Age 25 to 34 | 6.8% | 9.2% | 13.8% |
| Age 35 to 44 | 10.8% | 11.4% | 12.9% |
| Age 45 to 54 | 10.2% | 13.8% | 12.6% |
| Age 55 to 59 | 10.3% | 9.1% | 6.7% |
| Age 60 to 64 | 10.8% | 9.0% | 6.3% |
| Age 65 to 74 | 16.0% | 9.4% | 9.6% |
| Age 75 to 84 | 5.2% | 5.8% | 4.5% |
| Age 85 and over | 2.2% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Williamstown, MI | South Lyon, MI | United States |
| White | 94.8% | 89.9% | 59.4% |
| Black | 0.3% | 0.6% | 12.2% |
| Asian | 1.2% | 2.8% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.0% | 0.4% |
| Two or More Races | 2.1% | 4.1% | 3.2% |
| Hispanic | 1.4% | 2.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Williamstown, MI | South Lyon, MI | United States |
| Married Population | 63.5% | 53.9% | 49.8% |
| Currently Married | 63.5% | 53.3% | 48.0% |
| Married but Separated | 0.0% | 0.6% | 1.8% |
| Single Population | 36.5% | 46.1% | 50.2% |
| Never Married | 20.6% | 25.9% | 33.8% |
| Divorced | 8.8% | 14.1% | 10.8% |
| Widowed | 7.1% | 6.1% | 5.6% |
| space5 | | | |
| Household Size | 2.57 | 2.31 | 2.60 |
| Households | 2,047 | 5,074 | 124,010,992 |
| Family Households | 1,511 | 3,170 | 80,755,759 |
| Married couple, w/children | 31.0% | 29.4% | 30.5% |
| Married couple, no children | 58.5% | 49.8% | 42.9% |
| Non Family Households | 536 | 1,904 | 43,255,233 |
| Single householder, w/children | 6.9% | 13.4% | 15.8% |
| Single householder, no children | 3.6% | 7.4% | 10.8% |